1. Field of the Invention
The present invention relates to an internal combustion engine wherein fuel injection is controlled by an electronic system.
2. Description of the Prior Art
In an internal combustion engine wherein the fuel injection is controlled by an electronic system, the amount of the fuel to be injected is calculated in accordance with signals from intake air and other engine sensors. Fuel injectors are operated for a period corresponding to the calculated fuel amount and in synchronism with crank angles.
A typical intake air sensor is a so-called airflow meter. The response speed of air flow, however, is slow when the throttle valve is opened at a higher-than-predetermined speed. This delay results in a shortage of fuel during engine acceleration. To overcome this problem, it has been proposed to detect engine acceleration states and operate the fuel injectors at periods nonsynchronous with the crank angle, so as to enable a sufficient fuel supply from the start of acceleration despite the delayed response. In this case, however, a large nonsynchronous injection is necessary when the acceleration is effected just before or just after synchronized injections. Such a large nonsynchronous injection results in the presence of excess fuel in some cylinders during acceleration other than at the above times.
This occurs due to the following reason. In a multicylinder engine, a separate fuel injector is provided for each cylinder. Some or all of the injectors are simultaneously operated at predetermined crank angles, such as 360.degree.. A complete engine cycle corresponds to a crank angle of 720.degree..
On the other hand, the intake stroke occupies a crank angle of 180.degree.. Thus, in a four-cylinder engine, each cylinder receives two fuel injections from the end of one of its intake strokes to the end of its next intake stroke.
In the prior art electronically controlled fuel injection engine, in addition to the two fuel injections, cylinders would also receive nonsynchronous injections due to acceleration. Such nonsynchronous fuel injections, however, would not only affect the intake stroke of one cylinder directly after the acceleration, but also the succeeding intake stroke of another cylinder, due to the above mentioned facts.
If the acceleration does not occur just before or after a synchronous fuel injection, however, the synchronous fuel injection after the nonsynchronous fuel injection will take place with an amount of air from the air flow meter while the meter has begun its response. The additional amount of fuel from the nonsynchronous fuel injection then causes excess combustion in the cylinder, resulting in decreased output.